1. Field of the Invention
The present disclosure relates to a stereoscopic image display device, and more particularly, to a stereoscopic image display device which has the improved up and down viewing angles.
2. Discussion of the Related Art
Recently, due to developments of various video contents, stereoscopic image display devices which the user can select the display type (two or three dimensional) has been introduced. The three-dimensional display can be accomplished using the stereoscopic technique or the autostereoscopic technique.
The stereoscopic technique uses a binocular disparity due to a separation distance between the eyes. This type of stereoscopic technique can be divided into the glasses type and the glasses-free type. Further, the glasses type can be divided into the shutter glasses type and the patterned retarder type.
The patterned retarder type display device accomplishes three-dimensional display by using polarization properties of the patterned retarder on the display panel and those on the glasses. This type of display device alternately displays a right-eye image and left-eye image on the display panel, and switches the polarizing properties from the polarizing glasses though the patterned retarder. The viewer combines the transmitted left-eye and the right-eye images respectively and realizes a three-dimensional stereoscopic image. The patterned retarder type display has advantages in having small cross-talk between two eyes and in having good display quality of high brightness compared to other types.
FIG. 1 is a cross-sectional view of a patterned retarder type stereoscopic image liquid crystal display device according to the related art.
As shown in FIG. 1, the display device 1 includes an array substrate 130 having a thin film transistor, a color filter substrate 160 having black matrixes 155, a liquid crystal layer 140 between the array substrate 130 and the color filter substrate 160, and patterned retarder films 190 on the color filter substrate 160.
The black matrix includes a plurality of first black matrix lines and a plurality of second black matrix lines. The first black matrix lines are formed in the same direction of the gate line of the array substrate 130, and the second black matrix lines are formed in the same direction of the data line. The first and second black matrix lines define pixel areas by crossing each other.
The retarder films have first and second patterned retarders 191a and 191b, the polarization axes of which are different from each other. The first and second patterned retarders 191a and 191b are disposed line by line in turn. Specifically, the retarders 191a and 191b are alternately disposed along the lines how the unit pixels are continuously and straightly disposed. One of the first and second patterned retarders 191a and 191b is for displaying left-circularly polarized light and the other is for right-circularly polarized light.
Since the retarders 191a and 191b are disposed line by line in turn and alternately display left-eye image and right-eye image, a three-dimensional (3D) cross-talk can occur according to the viewing positions. Especially, when users see the device in the front direction, left-eye image and right-eye image from near upper or lower ends of the display screen can be displayed through the same patterned retarder. As a result, there occurs a cross-talk phenomenon that the left-eye and right-eye images may pass the left-eye lens of the polarization glasses at the same time. Although in the flat panel display device, each pixel has a black matrix, but its size is not sufficient to prevent the cross-talk.
By enlarging the width of the black matrix, the viewing angle can be broadened and the 3D cross-talk can be prevented from occurring. However, this method results in lowering opening aperture ratio and brightness of the front side. Thus, the display becomes dark and proper chroma is difficult to obtain. Further, when the display device displays 2D images, the display quality gets worse owing to the lowered opening aperture ratio.
To solve the above problems, it is suggested adopting a black stripe on the black matrix, which is shown in FIG. 2.
As shown in FIG. 2, since the black stripe 185 is formed on the black matrix 155, the left-eye image may, for instance, be prevented from passing through the second patterned retarder 191b. Also, the right-eye image may be prevented from passing through the first patterned retarder 191a. 
However, even in this configuration, the cross-talk error may still occur depending on a viewer's viewing position, and a compensation structure is still necessary. In particular, the cross-talk error that occurs near an upper and lower end of the display screen still offers problems.
Meanwhile, during manufacturing process when the patterned retarder film is pulled tightly before being attached to the polarization plate, the length of the patterned retarder film or total pitch may be different from the desired length. For instance in case of big sized display such as TV, the difference or error is about 150 micrometers at maximum, and in case of the smaller sized display device, the difference is about 70 micrometers. Further, while the retarder film is being attached to the polarization plate, attaching error can occur, as for TV, the error can be 50 micrometers at maximum, and as for the IT device, the error can be 25 micrometers at maximum.
If the total pitch error and the attaching error occur, the occurrence of the cross-talk can not be avoided, since the cross-talk results from minute scale. Thus high quality of display is difficult to achieve.